Piezoelectric Accelerometer with Wake Function

ABSTRACT

A sensor device that senses proper acceleration. The sensor device includes a substrate, a spacer layer supported over a first surface of the substrate, at least a first cantilever beam element having a base and a tip, the base attached to the spacer layer, and which is supported over and spaced from the substrate by the spacer layer. The at least first cantilever beam element further including at least a first layer comprised of a piezoelectric material, a pair of electrically conductive layers disposed on opposing surfaces of the first layer, and a mass supported at the tip portion of the at least first cantilever beam element.

CROSS REFERENCED APPLICATIONS

This application incorporates by reference the entire contents of eachof the following application: U.S. Provisional Patent Application Ser.No. 63/177,754, filed on Apr. 21, 2021, and entitled “PiezoelectricAccelerometer with Wake Function”.

BACKGROUND

This invention relates to accelerometers that measure properacceleration, the acceleration of a body in its own instantaneous restframe, and in particular voice accelerometers.

Piezoelectric and capacitive accelerometers are well known. Capacitiveaccelerometers are a type of accelerometer that uses capacitive sensingto measure proper acceleration and is generally considered as theprimary technology used in many markets and devices such as consumerelectronics, automotive air bag sensors, navigation systems, gamingdevices, etc. Piezoelectric accelerometers, on the other hand, have lessapplications while still having unique advantages over capacitiveaccelerometers.

Piezoelectric accelerometers use the “piezoelectric effect” of apiezoelectric material to measure dynamic changes in properacceleration.

Some of the advantages of piezoelectric accelerometers include beinginsensitive to dust and particles and being able to output a signalwithout the need for a bias voltage applied to the piezoelectricelement. Another advantage of piezoelectric sensor elements is that theelements can have a relatively large dynamic range because the elementsare not limited by either a capacitive gap size or an overlap ofinterdigitated elements.

SUMMARY

Some of the advantages of piezoelectric accelerometers makepiezoelectric accelerometers ideal for specific applications. Becausepiezoelectric accelerometers are relatively insensitive to dust andparticles, piezoelectric accelerometers can be packaged with otherdevices such as sensors that are exposed to real-world environments. Inaddition, because a piezoelectric accelerometer outputs a signal withoutthe need for a bias voltage applied to the piezoelectric element,piezoelectric elements are ideal for use as wake-up sensors.

One challenge with optimizing a piezoelectric accelerometer involvesmechanical shock.

The typical accelerometer device used in consumer electronics, military,or automotive systems may experience relatively high mechanical shocklevels, typically of 10,000 g or more, where “g” is standardacceleration due to gravity (9.8 m/s² or 32.17405 ft./s²). Becausepiezoelectric sensors produce output signals that are nearly linear, ashock of 10,000 g will impart about 10,000 times the stress into thepiezoelectric material of the piezoelectric element, as an accelerationof 1 g.

On the other hand, the piezoelectric material has a given materialstrength, i.e., so called “ultimate strength,” i.e., the maximum stressthat a material can withstand while being stretched or pulled before thematerial will fracture. Therefore, in a piezoelectric element that isused in a piezoelectric accelerometer, an applied stress to the materialdirectly produces a output voltage signal. Thus, in a linear device suchas piezoelectric accelerometer, there is an inherent trade-off betweenoutput signal and mechanical shock survivability.

According to an aspect, a sensor device includes a substrate, a spacerlayer supported over a first surface of the substrate, at least a firstcantilever beam element having a base and a tip, the base attached tothe spacer layer, and which at least first cantilever beam element issupported over and spaced from the substrate by the spacer layer, withthe at least first cantilever beam element tapering in width from thebase portion to the tip portion, and with the at least first cantileverbeam element including at least a first layer comprised of apiezoelectric material and a pair of electrically conductive layersdisposed on opposing surfaces of the first layer.

Some of the features that can be included in the above aspect can be oneor more or a combination of the following features or other featuresdisclosed below.

The piezoelectric material is aluminum nitride or lead zirconatetitanate or scandium-doped aluminum nitride. The substrate is silicon,the spacer is silicon dioxide and the pair of electrically conductivelayers are comprised of a refractory metal.

The at least first layer of piezoelectric material and the at leastfirst pair of electrically conductive layers are a plurality of layersof piezoelectric material and a plurality of electrically conductivelayers disposed on opposing surfaces of the plurality of piezoelectriclayers, and which plurality of layers of piezoelectric material andplurality of electrically conductive layers are arranged in a stack. Thecantilever beam element is configured to have an electricaldiscontinuity in the electrically conductive layers to provide anelectrically active portion of the cantilever beam element and anelectrically inactive portion of the cantilever beam element.

The sensor device includes plural cantilever beam elements that includesthe first cantilever beam element and a plurality of mass elementssupported at the tip portions of the cantilever beam elements whereinthe mass is supported on the electrically inactive portion of thecantilever beam element.

The at least first cantilever beam element is a plurality of cantileverbeam elements arranged in a close-packed area by interdigitating theplurality of cantilever beam elements. Each of the plurality ofcantilever beam elements has an electrical discontinuity in at least oneof the pair of electrically conductive layers to provide an electricallyactive portion and an electrically inactive portion.

Each of the plurality of cantilever beam elements has a mass element,with the mass element supported on the electrically inactive portion ofthe cantilever beam element. The sensor device includes pluralcantilever beam elements that includes the first cantilever beam elementand a single mass supported on the electrically inactive portion of theplural cantilever beam elements.

The sensor device further includes a plurality of cantilever beamelements including the first cantilever beam element, with the pluralityof cantilever beam elements arranged in a close-packed area, and witheach of the cantilever beam elements comprising at least the first layerof piezoelectric material, the pair of electrically conductive layers;and each further including a mass supported at the tip portion of thecantilever beam element.

The plurality of cantilever beam elements are electrically connected inseries with each.

According to an additional aspect, a voice accelerometer device includesa sensor device having a bandwidth of at least 1 kHz to produce anoutput signal and a detector circuit configured to receive the outputsignal from the sensor device and produce an output signal.

Some of the features that can be included in the above aspect can be oneor more or a combination of the following features or other featuresdisclosed below.

The voice accelerometer wherein the sensor device includes a substrate,a spacer layer supported over a first surface of the substrate, at leasta first piezoelectric cantilever beam element having a base portion thatis supported over the substrate and spaced from the substrate by thespacer layer, with the piezoelectric material being aluminum nitride orlead zirconate titanate or scandium-doped aluminum nitride, and thesubstrate being silicon, the spacer being silicon dioxide and the pairof electrically conductive layers comprised of a refractory metal.

The at least first cantilever beam element has a constant width from thebase portion to a tip portion, and with the cantilever beam elementincluding at least a first piezoelectric layer, a pair of electricallyconductive layers disposed on opposing surfaces of the firstpiezoelectric layer. The at least first layer of piezoelectric materialand the at least first pair of electrically conductive layers are aplurality of layers of piezoelectric material and a plurality ofelectrically conductive layers disposed on opposing surfaces of theplurality of piezoelectric layers, and which plurality of layers ofpiezoelectric material and plurality of electrically conductive layersare arranged in a stack.

The cantilever beam element has an electrical discontinuity in at leastone of the pair of electrically conductive layers to provide anelectrically active portion of the cantilever beam element and anelectrically inactive portion of the cantilever beam element. The voiceaccelerometer further includes a mass supported at the tip portion ofthe at least first cantilever beam element, with the mass supported onthe electrically inactive portion of the cantilever beam element.

The at least first cantilever beam element is a plurality of cantileverbeam elements arranged in a close-packed area by interdigitating theplurality of cantilever beam elements, and with each of the plurality ofcantilever beam elements having an electrical discontinuity in at leastone of the pair of electrically conductive layers to provide anelectrically active portion and an electrically inactive portion. Eachof the plurality of cantilever beam elements has a mass elementsupported on the electrically inactive portion of the cantilever beamelement.

According to an additional aspect, a packaged micro electromechanicalsystem (MEMS) device includes a MEMS device including a package having acompartment; and a MEMS die disposed in the compartment, the MEMS diesupporting a MEMS accelerometer and a MEMS microphone.

Some of the features that can be included in the above aspect can be oneor more or a combination of the following features or other featuresdisclosed below.

The packaged MEMS device further includes a circuit coupled to an outputof the MEMS accelerometer and an output of the MEMS microphone, with thecircuit functioning to combine output signals from the MEMSaccelerometer and the MEMS microphone into a single, combined outputsignal. The packaged MEMS device further includes a first band-passfilter coupled to the output of the MEMS accelerometer and a secondband-pass filter coupled to the output of the MEMS microphone.

The first band-pass filter has cut-off frequencies of about 100 Hz and2000 Hz; and the second band-pass filter has cut-off frequencies ofabout 2000 Hz and 8000 Hz. The packaged MEMS device further includes afirst amplifier coupled to the first band-pass filter that providessignal gain to the signal from the first band-pass filter and a secondamplifier coupled to the second band-pass filter that provides signalgain to the signal from the second band-pass filter.

The packaged MEMS device further includes a circuit that combines thesignals from the first and second amplifier into a single output signal.The packaged MEMS device senses both acceleration and sound produced bya user's voice. The packaged MEMS a pair of earbuds, with the MEMSaccelerometer used to sense vibrations from the vocal cords and the MEMSmicrophone used to sense acoustic sound through the air.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 1A are plan views of an exemplary piezoelectricaccelerometer sensor device.

FIG. 2 is a plan view of a piezoelectric element disposed in thepiezoelectric accelerometer sensor device of FIG. 1.

FIG. 2A is a cross-sectional view of the piezoelectric element of FIG.2, taken along line 2A-2A of FIG. 2.

FIG. 2B is the cross-sectional view of FIG. 2 showing an alternativeimplementation.

FIG. 3 is a plan view of an alternative piezoelectric element in thepiezoelectric accelerometer of FIG. 1.

FIG. 3A is a cross-sectional view of the alternative piezoelectricelement of FIG. 3, taken along line 3A-3A of FIG. 3.

FIGS. 3B and 3C are cross-sectional views of FIG. 3 showing alternativeimplementations.

FIGS. 3D to 3I are plan views showing other alternative implementations.

FIG. 3J is a plot of stress vs. base width.

FIG. 4 is a diagrammatical view of an illustrative earbud headphone.

FIG. 4A is a blown up view of a portion of FIG. 4.

FIG. 5 is a voice accelerometer.

FIG. 6 is a block diagram of an embedded processing device.

FIG. 7 is a diagram of a packaged MEMS device.

FIG. 8 is a block diagram of a ASIC useful in the MEMS device of FIG. 7.

DETAILED DESCRIPTION

Piezoelectric devices have an inherent ability to be actuated bystimulus even in the absence of a bias voltage due to the so called“piezoelectric effect” that cause a piezoelectric material to segregatecharges and provide a voltage potential difference between a pair ofelectrodes that sandwich the piezoelectric material. This physicalproperty enables piezoelectric devices to provide ultra-low powerdetection of a wide range of stimulus signals.

Micro Electro-Mechanical Systems (MEMS) can include piezoelectricdevices and capacitive devices. Accelerometers fabricated as capacitivedevices require a charge pump to provide a polarization voltage, whereaspiezoelectric devices such as piezoelectric accelerometers do notrequire a charge pump. The charge generated by the piezoelectric effectis generated due to stimulus causing mechanical stress in the material.As a result, ultra-low power circuits can be used to transfer thisgenerated charge through simple gain circuits.

Referring now to FIG. 1, a piezoelectric accelerometer sensor device 10includes a piezoelectric sensor element 12 as shown. In FIG. 1, thepiezoelectric sensor element 12 has a plurality of tapered cantileverbeam elements 14 a-14 n. The tapered cantilever beam elements 14 a-14 nhave respective base portions 15 a-15 n and tip portions 17 a-17 n. Thetapered cantilever beam elements 14 a-14 n are closely packed into adefined area by interdigitating successive ones of the taperedcantilever beam elements 14 a-14 n.

In this embodiment of the piezoelectric accelerometer sensor device 10the piezoelectric sensor element 12 includes 14 interdigitatedcantilevers elements 14 a-14 n. A greater or lesser number of cantileverbeam elements can be provided. A first one 14 a of the taperedcantilever beam elements 14 a-14 n has the base 15 a supported at afirst edge 16 a of the piezoelectric accelerometer sensor device 10 andhas the tip portion 17 a at a second edge 16 b of the piezoelectricaccelerometer sensor device 10. An immediately adjacent one 14 b of thetapered cantilever beam elements 14 a-14 n is interdigitated with thefirst one 14 a of the tapered cantilever beam elements 14 a-14 n, andwhich adjacent one 14 b of the tapered cantilever beam elements 14 a-14n has the base 15 b supported on the second, opposing edge 16 b of thepiezoelectric accelerometer sensor device 10 and has the tip at thefirst edge 16 a of the piezoelectric accelerometer sensor device 10.

Each of the tapered cantilever beam elements 14 a-14 n has its base 15a-15 n portion supported on and attached to the respective one of thefirst 16 a or second edges 16 b of the piezoelectric accelerometersensor device 10. Electrically conductive members (generally 20) areshown successively coupling alternating ones of the tapered cantileverbeam elements 14 a-14 n, in an electrically series arrangement into oneof a pair of groupings.

FIG. 1A shows a screen shot of the piezoelectric accelerometer sensordevice 10 that includes the piezoelectric sensor element 12 as generallyshown in FIG. 1.

Referring now to FIG. 2, the cantilever beam element 14 a that is partof the piezoelectric sensor element 12 of the piezoelectricaccelerometer sensor device 10 (FIG. 1) is shown. The cantilever beamelement 14 a is representative of each of the cantilever beam elements14 a-14 n. The cantilever beam element 14 a has a wide base region 15 aattached to a silicon substrate 42, which base region 15 a tapers to anarrow neck region 24 a. The stress in this tapering region isapproximately constant, and much higher than in the rest of thecantilever beam element 14 a. The width of the cantilever beam element14 a expands starting at the neck region 24 a to a wide region 26 a, andfrom the wide region 26, tapers to a tapering region 28 a and narrows toa rounded tip 17 a, e.g., a rounded tip. In some embodiments, thecantilever beam elements 14 a-14 n each have active regions 46 a-46 nand passive regions 48 a-48 b, as discussed below.

Referring now also to FIG. 2A, the cantilever beam element 14 a is shownin cross-section. The cantilever beam element 14 a includes a firstconductive layer 30 a disposed over a first piezoelectric layer 32 a, asecond conductive layer 34 a disposed over a second piezoelectric layer36 a, and a third conductive layer 38 a disposed over a spacer layer 40.The spacer layer 40 is on the substrate 42. The spacer layer 40positions the cantilever beam 14 a over the substrate 42 (whichsubstrate 42 can be substantially removed beyond the part of thecantilever beam attached to the substrate), but not touching thesubstrate 42 in a quiescent state. The cantilever beam element 14 a hasa break 44 a in the first conductive layer 30 a, a break 44 b in thesecond conductive layer 34 a and a break 44 c in the third conductivelayer 38 a disposed over a first spacer layer 40. The breaks 44 a-44 care electrically isolating regions (e.g., removed portions of therespective conductive layers 30 a, 34 a and 38 a), which may be filledin with piezoelectric layer portions 36 a-36 c. The breaks 44 a-44 cprovide an active portion 46 a of the cantilever beam element 14 a andan inactive portion 48 a of the cantilever beam element 14 a. Similaractive 46 b-46 n and inactive 48 b-48 n portions are provided for theother cantilever beam elements 14 b-14 n. (Alternatively, those inactiveportions of the conductive layers need not be applied to the cantileverbeam elements 14 a-14 n.)

Referring to FIG. 2B, an alternative configuration of FIG. 2A is shownwith the substrate 42 portion substantially removed. The remainingfeatures of FIG. 2B are as in FIG. 2A and need not be repeated here.

Referring to FIG. 3, an alternative cantilever beam element 14 a′ thatcould be an alternative implementation for all of the cantilever beamelement 14 a-14 n (FIG. 1) for the piezoelectric sensor element 12 ofthe piezoelectric accelerometer sensor device 10 (FIG. 1) is shown. Thecantilever beam element 14 a′ is similar to the cantilever beam element14 a of FIG. 2, having the wide base region 15 a attached to a siliconsubstrate 42, which base region 15 a tapers to a narrow neck region 24a. The stress in this tapering region is approximately constant, andmuch higher than that in the rest of the cantilever beam element 14 a′.The width of the cantilever beam element 14 a expands starting at theneck region 24 a to a wide region 26 a, and from the wide region 26, atapering region 28 a narrows to the rounded tip 17 a. The cantileverbeam element 14 a′ has a mass element 50 supported on conductive layer30 a. Other locations for the mass element 50 are feasible.

Referring now also to FIG. 3A, the cantilever beam element 14 a′includes the first conductive layer 30 a disposed over the firstpiezoelectric layer 32 a, the second conductive layer 34 a disposed overthe second piezoelectric layer 36 a, and the third conductive layer 38 adisposed over the first spacer layer 40. The spacer layer 40 is on thesubstrate 42, as discussed above for FIG. 2A.

The cantilever beam element 14 a′ also has the break 44 a in the firstconductive layer 30 a, the break 44 b in the second conductive layer 34a and the break 44 c in the third conductive layer 38 a. The breaks 44a-44 c are electrically isolating regions (e.g., removed portions of therespective conductive layers 30 a, 34 a, 38 a), which may be filled inwith piezoelectric layer portions 32 a, 36 a. The breaks 44 a-44 cprovide the active portion 46 a of the cantilever beam element 14 a′ andthe inactive or passive portion 48 a of the cantilever beam element 14a. (Similarly active and inactive portions are provided for the othercantilever beam elements (e. g., the cantilever beam elements 14 b-14 n,as illustrated for FIG. 1.)

In all material respects the cantilever beam element 14 a′ is the sameas cantilever beam element 14 a (FIG. 1) except that the cantilever beamelement 14 a′ has the mass element 50 supported on conductive layer 30 ain that portion of the conductive layer 30 a that is part of theinactive portion 48 a of the cantilever beam element 14 a′.

Referring to FIG. 3B, an alternative configuration of FIG. 3A is shownwith the substrate 42 portion substantially removed. The remainingfeatures of FIG. 3B are as in FIG. 3A and need not be repeated here.

Referring to FIG. 3C, another alternative configuration of FIG. 3A isshown with the substrate 42 portion and spacer 40 layers partiallyremoved, leaving portions 40 a, 40 b of the spacer and portions 42 a, 42b of the substrate. Portions 40 a, 40 b anchor the cantilever beamelement 14 a′ whereas, portions 40 b, 42 b are attached to the bottom ofthe cantilever beam element but do not anchor the cantilever beamelement 14 a′. The remaining features of FIG. 3C are as in FIG. 3A andneed not be repeated here.

Referring to FIG. 3D, another alternative configuration of FIG. 3A isshown with a single mass 52 over two cantilever beam elements 14 a′, 14c′ as shown. In addition, the spacer and the substrate can be partiallyremoved, leaving portions 40 a, 40 b of the spacer and portions 42 a, 42b of the substrate. Portions 40 a, 40 b anchor the cantilever beamelement 14 a′, 14 c′ whereas, portions 40 b, 42 b are attached to thebottom of the cantilever beam elements but do not anchor the cantileverbeam elements. The cantilevers taper from their respective baseportions. The free ends of the cantilevers are connected to one singlemass 52. Although this view only shows two cantilevers, more could beused. The mass 52 a portion of the silicon substrate affixed to thebottom portions of the cantilever elements 14 a′ 14 c′. The cantileverbeam elements are not interdigitated. The remaining features of FIG. 3Dare as in FIG. 3A, but without the cantilever beam elements 14 b′, 14 d′etc., and need not be repeated here.

The piezoelectric accelerometer sensor device 10 with the piezoelectricsensor element 12 optimizes an output signal of the piezoelectricaccelerometer sensor device 10 for a selected mechanical shocksurvivability limit.

In order to accomplish shock level optimization, the piezoelectricsensor element 12 optimizes stress distribution. This stressdistribution optimization results from recognizing that the outputsignal that is optimized is not simply output voltage (or sensitivity),but is actually output energy (E), and that for a given accelerationlevel, the output energy (E) is defined as:

$E = {\frac{1}{2} \cdot C \cdot V^{2}}$

where C is the device capacitance and V is the output voltage.

Given that the output energy is proportional to C·V² the piezoelectricaccelerometer sensor device 10 has the piezoelectric sensor element 12configured to distribute or spread, uniformly, a high stress level thatcould result from, e.g., a mechanical shock across a large surface areaand thus avoid stress peaks that could cause the material of thepiezoelectric sensor element 12 to fracture.

This uniform distribution of stress is provided by several mechanisms.One mechanism, as illustrated in FIGS. 2, 2A, 2B above, involves thetapered cantilever beams 14 a-14 n having active portions 46 a-46 n thatare used in producing the electrical output signals from each of thecantilever beams 14 a-14 n resulting accelerations sensed by thepiezoelectric sensor element 12, and passive portions 48 a-48 n that areelectrically isolated from the active portions 46 a-46 n and, thus, haveno role in producing the electrical output signals resulting from thepiezoelectric sensor element 12 sensing acceleration, but which passiveportions 48 a-48 n increase the mass of the tapered cantilever beams 14a-14 n, as illustrated in FIGS. 2, 2A, 2B above.

Another mechanism, as illustrated in FIGS. 3, 3A-3D above, involves thetapered cantilever beam 14 a′ and (analogs of the cantilever beams 14b-14 n as in FIG. 2) having the active portions 46 a-46 n from whichelectrical output signals are provided, and having the passive portions48 a-48 n that are electrically isolated from the portions 46 a-46 n,and play no role in producing the electrical output signals resultingfrom the piezoelectric sensor element 12 sensing acceleration, but whichpassive portions 48 a-48 n each carry the added mass 50 at the tipportions of the tapered cantilever beams 14 a-14 n, and which furtherincreases the mass of the tapered cantilever beams 14 a-14 n.

Another mechanism involves using a denser material at the tip end or theinactive portions of the tapered cantilever beams 14 a-14 n.

A uniform stress level can be provided by tapering a cantilever with amass at the tip. In a cantilever of uniform width with a mass placed atits tip, the peak stress is located at the base and the stress graduallyreduces from the base to the tip. By making the base wider than the tip,the stress in the material can be uniform across the entire structure.Further, these cantilever beams can be closely packed into a given areaby interdigitating these tapered cantilever beams 14 a-14 n.

In general, these mechanisms are or can be used together. That is, thetapered cantilever beams 14 a-14 n have the active portions and thepassive portions. The passive portions 48 a-48 n of the taperedcantilever beams 14 a-14 n carry the added mass, and in someembodiments, either the passive portions 48 a-48 n and/or the added massare comprised of a thicker and/or more dense material than the activeportions 46 a-46 n of the tapered cantilever beams 14 a-14 n. Using amore dense material can minimize the area supporting the added mass.

As more mass is added to ends of the tapered cantilever beams 14 a-14 n,the resonance frequency of the tapered cantilever beams 14 a-14 ndecreases, and the mechanical stress in the material increases. It isdesirable to minimize the area consumed by this added mass in order tomaximize the area used for the active part of the sensor. Thus, asmentioned above, using a denser material than the active portion or athicker material will tend to minimize the area used by the mass. Inthis way, a more complex process with additional layers can lead toimproved performance for a given sensor area by increasing the massdensity. For example, by adding a thick metal layer such as aluminum tothe tip of the plates, the sensitivity can be increased. Another examplewould be adding a portion of the substrate (Si) to the non-activeportion of the cantilever beam element 14 a. Other examples arepossible.

The tapered cantilever beams 14 a-14 n each are comprised of threeelectrode layers 30 a, 34 a, 38 a sandwiching two piezoelectric layers32 a, 36 a. In other embodiments, the tapered cantilever beams can befewer than or more than fourteen cantilever beams. In other embodiments,the tapered cantilever beams can be comprised of more than threeelectrode layers sandwiching more than two piezoelectric layers, e.g.,four electrode layers sandwiching three piezoelectric layers, etc.

Suitable materials for the electrodes layers include refractory metalssuch as molybdenum (Mo) titanium, vanadium, chromium, tungsten,zirconium, hafnium, ruthenium, rhodium, osmium and iridium, and metalssuch as platinum. Suitable piezoelectric materials include aluminumnitride (AlN). Other piezoelectric materials could be used, such as leadzirconate titanate (PZT). One specific combination is Mo and AlN, butSc-AlN (Scandium-doped Aluminum nitride and PZT could be used in placeof AlN). The electrodes have a discontinuity about half way down thelength of the cantilever. This discontinuity separates the portion ofthe beam that electrically contributes to the output from that whichdoes not. The portions that actively contribute to the output arereferred to above as the active portions 46 a-46 n or active areas, andthe portions that do not electrically contribute are referred to aboveas the passive 48 a-48 n or inactive portions or area.

The break between the active and inactive areas is along a line ofconstant stress (here, stress σ is defined as σ=σ_(xx)+σ_(yy)). Thedemarcation between active 46 a-46 n and inactive 48 a-48 n areas of thebeam are the lines of constant stress that maximize the output energy(E) given by (E=½·C·V²) for a given acceleration.

The fourteen cantilever beams 14 a-14 n are electrically connected inseries via conductors to increase the output voltage generated by thepiezoelectric sensor element 12 but at a lower capacitance forpiezoelectric sensor element 12.

In an illustrative example of the piezoelectric sensor element 12, thepiezoelectric sensor element 12 has fourteen cantilevers wired inseries. In the embodiment, the piezoelectric sensor element 12 iscomprised of Mo and AlScN and has an active length of 320 microns, aninactive length of 336 micron, and a width at its maximum width of 164microns. The piezoelectric sensor element 12 has two piezoelectricmaterial AlScN layers each having a thickness of 0.5 microns and the Moconductors have a thickness of 20 nano-meters. The piezoelectric sensorelement 12 of this example could produce an output voltage ofapproximately 1.6 mV/g (where g is gravitation acceleration) and acapacitance of approximately 1.27 pF. Of course, other examples could beused.

The piezoelectric sensor element 12 could provide an piezoelectricaccelerometer sensor device 10 having a resonance frequency ofapproximately 3 kHz, giving the piezoelectric accelerometer sensordevice 10 relatively more bandwidth of at least 1 kHz, than typicalpiezoelectric and/or capacitive based accelerometers, and thus suchpiezoelectric sensor element 12 could be used to provide a class ofaccelerometers commonly referred to as “voice accelerometers.” In otherembodiments the resonance frequency can be e.g., around 5 kHz.

These voice accelerometers, when placed into an earbud-style headset,sense voice by picking up the vibrations that are transmitted from thevocal chords, through the skull, to the headset while speaking.Typically, voice accelerometers are used to filter audio coming througha microphone or alone as voice pickup in noisy environments. Because thevoice accelerometer is much less sensitive to external noise than amicrophone, the voice accelerometer can be used to filter the microphonesignal and reduce background noise.

The piezoelectric sensor element 12 used in the piezoelectricaccelerometer sensor device 10 in combination with a low power wake-upcircuit can provide a low-power wake-up voice accelerometer. Asmentioned, this piezoelectric accelerometer outputs a voltage without aneed for a bias voltage or bias charge. Therefore, it can be combinedwith low power circuitry and function as a wake-up for a low powerheadset with a voice interface.

FIG. 4 shows an example of an earbud-style headset with ear buds(generally 62) that hold acoustic transducers and with a built in voiceaccelerometer (see FIG. 4A) and a package 64 that can contain volume,mute, answering, controls, etc. The style shown in FIG. 4 is exemplary,as any style can be used with the built in voice accelerometer. Theearbud-style headsets are typically powered by a rechargeable battery,and include Bluetooth or other wireless technology. In particular thesecan be used in the true wireless stereo versions of earbuds.

FIG. 4A shows a typical placement of the piezoelectric accelerometersensor device 10, used as a voice accelerometer that substitutes for abuilt-in microphone in one of the earbuds 62 of the headset 60. Theplacement is configured to sense voice by picking up the vibrationstransmitted from the vocal chords through the skull to the voiceaccelerometer in one (or both) of the earbuds 62 to the headset 60 whilethe user is speaking. In addition to the earbud 62, the earbud includesan acoustic transducer, e.g., speaker that is fed from an externalcircuit/device 64.

Referring now to FIG. 5, a low-power wake-up voice accelerometer 80 isshown. In order to provide a low-power wake-up voice accelerometer, alow power wake-up circuit 84 is coupled to receive an output signal fromthe voice accelerometer, as shown. The low-power wake-up voiceaccelerometer 80 includes the piezoelectric accelerometer sensor device10 (FIG. 1, FIG. 1A) a reduced size version of FIG. 1A is shown, (thedetails are not explained nor need to be illustrated in FIG. 5. For suchdetails the reader is referred to FIGS. 1-3A.

The output from piezoelectric accelerometer sensor device 10 is anoutput charge or voltage signal that is fed to a band pass filter BPF82. For a low-power wake-up voice accelerometer application, the bandpass filter 82 is used prior to comparing the signal from thepiezoelectric accelerometer sensor device 10 to a threshold, to filterout effects caused from low frequency motion that would be sensed by theaccelerometer and that would otherwise exceed the threshold. The outputfrom the band pass filter 82 is fed to an input of the low powerdetection circuit 84.

The detection circuit 84 includes a source follower stage 86 thattransforms charge generated by low-power wake-up voice accelerometer 80(post band pass filtering from band pass filter 82), and provides gainto the band pass filtered signal for the next stage (e.g., a latchedcomparator stage) 88. The latched comparator 88 includes a latchcomparator and is used to compare the output of the source follower 86stage to a reference voltage that is chosen to target a specific minimumacceleration level. Once this level has been sensed, the latchedcomparator 88 latches the event, and provides a signal indicating such.The latched comparator uses positive feedback to effectively act as amemory cell.

In a variation, latched comparator 88 is configured to detect when theacoustic input (or VIN) satisfies one or more specified criteria. Thereare various types of criteria that the detection circuit 80 can beconfigured to detect. These criteria include, e.g., voice criteria(detection of voice), keyword criteria (e.g., detection of keywords),ultrasonic criteria (e.g., detection of ultrasonic activity in proximityto our surrounding the transducer or acoustic device), criteria ofdetecting footsteps, mechanical vibrations/resonances, gunshots,breaking glass, and so forth.

In this example, a bandwidth of the preamplifier stage (e.g.,implemented by the preamplifier) determines a spectrum of input signalsthat trigger the comparator stage implemented by the latched comparator88. Ultra-Low Power electronics typically have bandwidths acceptable forthe audio range. Also, impulse events trigger a broad spectrum increasein energy, acceptable for triggering with the comparator.

Once power is removed from the latched comparator, the information thatwas latched is cleared or lost, while memory, e.g., static random accessmemory (SRAM) FIG. 6, retains the information even with the powerremoved. This signal DOUT is an output signal that is used for detectionof a signal at the requisite vibration level and, thus, used as awake-up signal for a voice accelerometer. This signal can be furtherused to control/trigger other events within an application specificintegrated circuit (ASIC) or within an overall system by using thissignal as an input to another system/device.

Referring now to FIG. 6, an example of an embedded processing device 90that can be used to process output DOUT (FIG. 5) includes aprocessor/controller 92 that can be an embedded processor, a centralprocessing unit or fabricated as an ASIC (application specificintegrated circuit), etc. The processing device 90 also includes memory94, storage 96 and I/O (input/output) circuity 98, all of which arecoupled to the processor/controller 92 via a bus 99. The I/O circuity98, e.g., receives the digitized output signal DO, processes that signaland generates a subsequent output that can be a wake-up signal or othersignal, as appropriate for external circuitry.

In some implementations, the processing device 90 performs the functionof a threshold detector to detect when an acoustic input to the voiceaccelerometer equals or exceeds a threshold level, e.g., by detectingwhen the DO equals or exceeds an amplitude level or is within afrequency band. Because in such an implementation detection is performedby the processing device 90, rather than being included in the acousticdevice, e.g., hybrid integrated voice accelerometer, the processingdevice 90 needs to remain powered on to detect the audio stimulus.

Referring now to FIG. 7, an illustrative example of a packaged MEMSdevice 100 is shown. The MEMS device 100 includes a package 102 having acompartment 104, with a circuit board 106 that supports a MEMS die 108.The MEMS die 108 has the piezoelectric accelerometer sensor device 10configured to provide a voice accelerometer and a MEMS microphone 112.Both the piezoelectric accelerometer sensor device 10 and the MEMSmicrophone 112 are connected to an application specific integratedcircuit (ASIC) 114.

The ASIC 114 functions to combine output signals from the MEMSpiezoelectric accelerometer sensor device 10 and the MEMS microphone 112into a single, combined output signal. The MEMS piezoelectricaccelerometer sensor device 10 and the MEMS microphone 112 are coupledto the (ASIC) 114, for example, by wire bonds 110 a, 110 b and 112 a,112 b, as shown. Also shown are other wire bonds (not referenced) thatcan be coupled to other circuit elements such as device circuity of adevice (not shown) that would incorporate the MEMS device 100, as wellas power connections, etc.

As mentioned above, the voice accelerometer signal is often combinedwith a microphone signal in order to provide a lower noiserepresentation of a user's voice. Some of the unique aspects of thepiezoelectric accelerometer sensor device 10 that makes it ideallysuitable for such an application include that the piezoelectricaccelerometer sensor device 10 is fabricated by the same process as themicrophone 112, while, at the same time, the piezoelectric accelerometersensor device 10 is relatively insensitive to dust particles, etc.,compared to an equivalent capacitive accelerometer.

The piezoelectric accelerometer sensor device 10 can be built on thesame MEMS die and packaged in the same MEMS package as the MEMSmicrophone 112. Furthermore, the piezoelectric accelerometer sensordevice 10 and the MEMS microphone 112 can share the same ASIC thatcombine the signals from the microphone and the accelerometer into asingle representation of the user's voice.

Referring now to FIG. 8, aspects of the ASIC 114 (FIG. 7) are shown.Salient features of the ASIC 114 include, for example, a band-passfilter 114 a that is coupled to the output of the piezoelectricaccelerometer sensor device 10 and which band-pass filter 114 a hascut-off or −3 dB frequencies of, for example, 100 Hz and 2000 Hz. Theband-pass filter 114 a has its output coupled to an amplifier 114 b thatprovides an appropriate amount of signal gain to the signal from theband-pass filter 114 a. The ASIC 114 also includes, for example, aband-pass filter 114 c that is coupled to the output of the MEMSmicrophone 112 and which band-pass filter 114 c has cut-off or −3 dBfrequencies of, for example, 2000 Hz and 8000 Hz. The band-pass filter114 c has its output coupled to an amplifier 114 d that provides anappropriate amount of signal gain to the signal from the band-passfilter 114 c.

The outputs from the amplifier 114 b and the amplifier 114 d arecombined, e.g., these signals could be coupled to a third amplifier 114e that combines these output signals into a single output signal(S_(out)) that represents a user's voice. Other approaches could beused.

The MEMS device 100 (FIG. 7) has the piezoelectric accelerometer sensordevice 10 fabricated by the same process as the microphone 112. The MEMSdevice 100 is packaged in a single package that houses both thepiezoelectric accelerometer sensor device 10 (that has a relatively highresonance frequency and optimized to withstand relatively highmechanical shock levels) and the microphone 112, and which share thesame MEMS die 108. This MEMS device 100 can sense both acceleration andsound produced by a user's voice, and thus improve the quality of asignal representative of the user's voice, as the piezoelectricaccelerometer sensor device 10 is acting as a voice accelerometer.

The MEMS device 100 that has the voice piezoelectric accelerometersensor device 10 can be fabricated by the same process as the microphone112, but does not necessarily need to combine their respective signals.For example, the MEMS device 100 could have, for example, separateamplifier stages for the voice piezoelectric accelerometer sensor device10 and the microphone 112, or the MEMS device 100 could use the voicepiezoelectric accelerometer sensor device 10 for wake-up and use themicrophone signal output for voice. Therefore, the MEMS device 100 couldhave two outputs, one for the voice piezoelectric accelerometer sensordevice 10 and one for the microphone 112. For example, the MEMS device100 can be part of a remote control with the MEMS piezoelectricaccelerometer sensor device 10 used to determine if the remote controlhas been picked up and the MEMS microphone 112 used for voice commands.A similar arrangement/use can be provide if the MEMS device 100 is usedin a smartphone, etc.

OTHER EXAMPLES

In some examples, it is desired to have the cantilevers elements 14 a-14n produce an increased amount of audio, relative to amounts of audioobtained using the foregoing techniques. In these examples, an increasedamount of audio is obtained by attaching (or hanging) a mass underneatha cantilever — as described in further detail below. This inclusion ofthe mass introduces particular types of stresses to cantilever beams, asfollows:

1. Film Stress Due to Acceleration that Produces a Higher Signal Level:The signal level (as described as vibration signal below) results from achange in film stress due to acceleration. This is desired because thepiezoelectric film gives an output proportional to the stress level inthe film - to obtain a higher output amplitude, more stress is placedinto the film. By adding more mass, the same acceleration puts morestress into the film for a given acceleration, therefore giving a higheroutput amplitude signal and increasing sensitivity. The mass helpsincrease sensitivity but makes the device more likely to break. Asdescribed below, cantilevers of constant width reduce the probability ofthis happening.

2. Buckling: Cantilevers elements 14 a-14 n of constant width reduce theprobability of the device breaking due to increased film stress cause byacceleration, as described above. In achieving this constant width, itis preferable to use a plurality of cantilevers with constant width,rather than using a single cantilever of constant width. This is becausea single cantilever of constant width is highly susceptible to buckling,e.g., stress resulting from either temperature variation or the residualstress in the film after deposition. Temperature variation leads to filmstress because the silicon substrate (and silicon mass) have a differentcoefficient of thermal expansion than the aluminum nitride that mostlymakes up the cantilever elements 14 a-14 n. Reducing the width of thecantilever elements 14 a-14 n and using a plurality of cantileverelements 14 a-14 n helps make them more resilient to buckling overstress variations.

3. Stress Due to Reliability Testing: While a given acceleration to putmore stress into the film is desired, the device also needs to passtypical reliability tests such as drop tests and mechanical shock tests.These tests can cause high acceleration levels (e.g., shocks) in anyorientation and so the piezoelectric accelerometer sensor device 10should be designed to ensure that these shocks do not cause the stressto get too high and the device to break. As described below, thecantilevers of constant width can help with this reliability, relativeto tapered cantilevers, especially when the mass hangs down from thecenter of the cantilever elements.

FIG. 3E is a variation of FIG. 3D. In this variation, substantiallystraight cantilevers connect to a single mass (also referred to hereinas a mass element). In this variation, a single mass 52′ that isattached underneath two substantially straight cantilever beam elements14 a″, 14 c″ is shown. Cantilever beam elements 14 a″, 14 c″ are alsoreferred to herein as cantilevers 14 a″, 14 c″ or beams or cantileveredbeams. By connecting several substantially straight cantilevers 14 a″,14 c″ to a single mass 52′, a chance of bucking is reduced (relative toa chance of buckling without connecting several substantially straightcantilevers 14 a″, 14 c″ to a single mass 52′) to allow for betterperformance over stress and temperature variations. In this example,“better performance” refers to an increase in obtained vibration signal(which, in turn, produces an increase in audio), relative to an amountof vibration signal obtained with less mass. The free ends of thecantilevers are connected to one single mass 52′. Although this viewonly shows two cantilevers, more could be used. The mass 52′ is affixedto the bottom portions of the cantilever elements 14 a″ 14 c″.

In this example, the mass 52′ provides for an increase in audioobtained, as follows: the sensitivity of the cantilevers is increasedbecause the output voltage is proportional to the stress in thepiezoelectric film. The larger mass produces more stress in thecantilever beams 14 a″, 14 c″, etc. for the same amount of acceleration.That is, an acoustic device, e.g., a piezoelectric accelerometer sensordevice 10 with this amount of mass and this configuration of cantileverbeams 14 a″ etc. is able to output more audio, relative to an amount ofaudio output with less mass. However, with this increase in mass, thereis an increase in mechanical stress on the cantilevered beams 14 a″etc., relative to an amount of stress when the mass is smaller. Also,because of the increase in audio, there is an increase in force acrossthe beams 14 a″ etc. To compensate for this increase in force andprovide for a more uniform stress level across the beams 14 a″ etc., thecantilevered beams are more rectangularly shaped, relative to the shapeof the cantilevered beams as shown in FIG. 3D, and have a particularwidth—as described herein. In some examples, this mass is comprised of asilicon die that is about or actually 50 microns thick more generally ina range of 40 microns to 70 microns.

As shown in FIG. 3F, cantilever beam 14 a″ has is a substantiallystraight beam that has mass 21 attached to bottom portion of cantileverbeam 14 a″. In this example, cantilever beam 20 includes a tip portion20 a and a base portion 20 b. The cantilever beam 20 is comprised of AlNand Mo. Generally, a base portion 20 b includes a portion of the beamthat is attached (either directly or indirectly, e.g., through thepreviously described spacer layer 40) to the substrate. Generally, a tipportion includes a portion of the beam that is further away from thebase portion, e.g., relative to a distance between the base portion andother portions of the beam. By attaching mass 21 to substantiallystraight beam 20, a piezoelectric accelerometer sensor device or othersensor device or transducer that includes cantilever beam 20 with mass21 is able to obtain an increased amount of signal (i.e., betterperformance, as previously described) that is reliable, with arelatively decreased amount of mechanical stress, relative to an amountof mechanical stress without the mass 21. The combination ofsubstantially straight cantilever beam 20 with mass 21 attached to thebottom of beam 20 provides for increased signal to noise ratio (SNR),relative to SNR with less mass An example of less mass would be the topaluminum layer in FIG. 3B, for example, which is approximately 1 umthick. In this example, mass 21 is silicon with a thickness of 50microns. This mass 21 produces the increase in signal. However, theincrease in signal results in an increased amount of mechanical stressacross the cantilever beams, relative to an amount of mechanical stresswith a smaller mass. As such, the width of the substantially rectangulardesign of the cantilever beam 20 attached to the mass allows thecantilever beam 20 to survive this increase is mechanical stress.

Referring to FIGS. 3G and 3H, substantially rectangular cantilever beams30 a-30 d are shown attached to mass 31. In these examples, only half ofthe beams are shown for a full transducer. In practice, another set ofbeams attached to another mass would face beams 30 a-30 d. As such inFIG. 3G, the cantilevered beams 30 a-30 d are separated out with gapsbetween the beams and are not just one wide cantilever. One widecantilever bean would have buckling due to the stress of the film. Byseparating out the cantilever beams 30 a-30 d, the cantilever beams 30a-30 d are less likely to buckle due to the residual stress in the filmafter deposition. Additionally, in this example, mass 31 is a siliconmass with a thickness between 25-50 microns. This results in more torque(˜400 microns) on the base of the cantilever beams 30 a-30 d. To ensurethat the cantilever beams 30 a-30 d are reliable with this increasedtorque, the cantilever beams 30 a-30 d have a constant width, e.g., 175μm in this modeled geometry. As previously described, this constantwidth improves reliability, relative to an amount of reliabilityachieved in these circumstances with tapered cantilever beams.

Referring to FIG. 3I, single cantilever beam 30 a, from which mass 31hangs, is shown. In this example, the width of cantilever beam 30 avaries, and in a particular example is 175 μm thickness. The thicknessof the film (e.g., Aluminum nitride (AlN) film shown in FIG. 3F) is tobe as thin as possible. In this example, the film has a thickness of 400nm or less. As is shown in FIG. 3G, the space between the cantileverbeams is ideally between 6 to 20 μm. In this example, it may bepreferable to use up as much space between the beams as possible, toprovide for even more uniform stress across the beams. Unlike designsthat have been described previously, this design provides for anincrease in signal due to the increase in mass 31 and addresses theissue of buckling, which results from high film stress in the asdeposited film or due to temperature variation, in combination with awide cantilever beam.

Referring to FIG. 3J, a stress window across the cantilever beams asfunction of the base width of the beam is shown. The stress window isthe stress at which the first tensile buckling mode occurs minus thestress at which the first compressive buckling mode occurs. Anacceptable stress window is substantially greater than 400 MPa. In thisexample, 400 MPa corresponds to ˜175 um width for the particulargeometry modeled.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A sensor device, comprises: a substrate; a spacerlayer supported over a first surface of the substrate; at least a firstcantilever beam element having a base and a tip, the base attached tothe spacer layer, and which at least first cantilever beam element issupported over and spaced from the substrate by the spacer layer, withthe at least first cantilever beam element having a substantiallyconstant width from the base portion to the tip portion, and with the atleast first cantilever beam element further comprising: at least a firstlayer comprised of a piezoelectric material; and a pair of electricallyconductive layers disposed on opposing surfaces of the first layer. 2.The sensor device of claim 1 wherein the piezoelectric material isaluminum nitride or lead zirconate titanate or scandium-doped aluminumnitride.
 3. The sensor device of claim 1 wherein substrate is silicon,the spacer is silicon dioxide and the pair of electrically conductivelayers are comprised of a refractory metal.
 4. The sensor device ofclaim 1 wherein the at least first layer of piezoelectric material andthe at least first pair of electrically conductive layers are aplurality of layers of piezoelectric material and a plurality ofelectrically conductive layers disposed on opposing surfaces of theplurality of piezoelectric layers, and which plurality of layers ofpiezoelectric material and plurality of electrically conductive layersare arranged in a stack.
 5. The sensor device of claim 1 wherein thecantilever beam element is configured to have an electricaldiscontinuity in the electrically conductive layers to provide anelectrically active portion of the cantilever beam element and anelectrically inactive portion of the cantilever beam element.
 6. Thesensor device of claim 1 further comprising: plural cantilever beamelements that includes the first cantilever beam element; and aplurality of mass elements supported at the tip portions of thecantilever beam elements wherein the mass is supported on theelectrically inactive portion of the cantilever beam element.
 7. Thesensor device of claim 1 wherein the at least first cantilever beamelement is a plurality of cantilever beam elements arranged in aclose-packed area by interdigitating the plurality of cantilever beamelements.
 8. The sensor device of claim 7 wherein each of the pluralityof cantilever beam elements has an electrical discontinuity in at leastone of the pair of electrically conductive layers to provide anelectrically active portion and an electrically inactive portion.
 9. Thesensor device of claim 8 wherein each of the plurality of cantileverbeam elements has a mass element, with the mass element supported on theelectrically inactive portion of the cantilever beam element.
 10. Thesensor device of claim 1 wherein the sensor device further comprises:plural cantilever beam elements that includes the first cantilever beamelement; and a single mass supported on the electrically inactiveportion of the plural cantilever beam elements.
 11. The sensor device ofclaim 1, further comprises: a plurality of cantilever beam elementsincluding the first cantilever beam element, with the plurality ofcantilever beam elements arranged in a close-packed area, and with eachof the cantilever beam elements comprising at least the first layer ofpiezoelectric material, the pair of electrically conductive layers; andeach further including a mass supported at the tip portion of thecantilever beam element.
 12. The sensor device of claim 7 wherein theplurality of cantilever beam elements are electrically connected inseries with each.
 13. A voice accelerometer device comprising: a sensordevice having a bandwidth of at least 1 kHz to produce an output signal;and a detector circuit configured to receive the output signal from thesensor device and produce an output signal.
 14. The voice accelerometerof claim 13 wherein the sensor device comprises: a substrate; a spacerlayer supported over a first surface of the substrate; at least a firstpiezoelectric cantilever beam element having a base portion that issupported over the substrate and spaced from the substrate by the spacerlayer, with the piezoelectric material being aluminum nitride or leadzirconate titanate or scandium-doped aluminum nitride, and the substratebeing silicon, the spacer being silicon dioxide and the pair ofelectrically conductive layers comprised of a refractory metal.
 15. Thevoice accelerometer of claim 13 wherein the at least first cantileverbeam element has a constant width from the base portion to a tipportion, and with the cantilever beam element including at least a firstpiezoelectric layer, a pair of electrically conductive layers disposedon opposing surfaces of the first piezoelectric layer.
 16. The voiceaccelerometer of claim 15 wherein the at least first layer ofpiezoelectric material and the at least first pair of electricallyconductive layers are a plurality of layers of piezoelectric materialand a plurality of electrically conductive layers disposed on opposingsurfaces of the plurality of piezoelectric layers, and which pluralityof layers of piezoelectric material and plurality of electricallyconductive layers are arranged in a stack.
 17. The voice accelerometerof claim 15 wherein the cantilever beam element has an electricaldiscontinuity in at least one of the pair of electrically conductivelayers to provide an electrically active portion of the cantilever beamelement and an electrically inactive portion of the cantilever beamelement.
 18. The voice accelerometer of claim 17 further comprising: amass supported at the tip portion of the at least first cantilever beamelement, with the mass supported on the electrically inactive portion ofthe cantilever beam element.
 19. The sensor device of claim 13 whereinthe at least first cantilever beam element is a plurality of cantileverbeam elements arranged in a close-packed area by interdigitating theplurality of cantilever beam elements, and with each of the plurality ofcantilever beam elements having an electrical discontinuity in at leastone of the pair of electrically conductive layers to provide anelectrically active portion and an electrically inactive portion. 20.The sensor device of claim 13 wherein each of the plurality ofcantilever beam elements has a mass element supported on theelectrically inactive portion of the cantilever beam element.
 21. Apackaged micro electromechanical system (MEMS) device comprises: a MEMSdevice including a package having a compartment; and a MEMS die disposedin the compartment, the MEMS die supporting a MEMS accelerometer and aMEMS microphone.
 22. The packaged MEMS device of claim 21 wherein thepackaged MEMS device further comprises: a circuit coupled to an outputof the MEMS accelerometer and an output of the MEMS microphone, with thecircuit functioning to combine output signals from the MEMSaccelerometer and the MEMS microphone into a single, combined outputsignal.
 23. The packaged MEMS device of claim 21 wherein the packagedMEMS device further comprises: a first band-pass filter coupled to theoutput of the MEMS accelerometer; and a second band-pass filter coupledto the output of the MEMS microphone.
 24. The packaged MEMS device ofclaim 23 wherein the first band-pass filter has cut-off frequencies ofabout 100 Hz and 2000 Hz; and the second band-pass filter has cut-offfrequencies of about 2000 Hz and 8000 Hz.
 25. The packaged MEMS deviceof claim 23 wherein the packaged MEMS device further comprises: a firstamplifier coupled to the first band-pass filter that provides signalgain to the signal from the first band-pass filter; and a secondamplifier coupled to the second band-pass filter that provides signalgain to the signal from the second band-pass filter.
 26. The packagedMEMS device of claim 25 wherein the packaged MEMS device furthercomprises: a circuit that combines the signals from the first and secondamplifier into a single output signal.
 27. The packaged MEMS device ofclaim 21 wherein the packaged MEMS device senses both acceleration andsound produced by a user's voice.
 28. The packaged MEMS device of claim21 wherein the MEMS device is a pair of earbuds, with the MEMSaccelerometer used to sense vibrations from the vocal cords and the MEMSmicrophone used to sense acoustic sound through the air.
 29. A sensordevice, comprises: a substrate; a mass element comprising silicon,wherein the mass element has a thickness of approximately fifty microns;and a plurality of cantilever beam elements each having a base portionand a tip portion, each bottom side of the base portion attached to thesubstrate such that each cantilever beam element attached to thesubstrate is spaced from one or more other cantilever beam elementsattached to the substrate, wherein each bottom side of the tip portionis attached to the mass element, and with each of the cantilever beamelements further comprising: at least a first layer comprised of apiezoelectric material; and a pair of electrically conductive layersdisposed on opposing surfaces of the first layer.
 30. The sensor deviceof claim 29, wherein a cantilever beam element has a width ofapproximately 175 μm.
 31. The sensor device of claim 29, wherein acantilever beam element has a width of less than 175 μm.
 32. The sensordevice of claim 29, wherein a cantilever beam element has asubstantially rectangular shape.
 33. The sensor device of claim 29,wherein the mass element is configured to increase the signal to noiseratio of the sensor device, relative to a signal to noise ratio of thesensor device without a mass element.
 34. The sensor device of claim 33,wherein a cantilever beam element is substantially rectangular in shapeand is dimensioned with a first width to decrease an amount of bucklingin the cantilever beam element, relative to an amount of buckling in arectangular shape cantilever beam element with a second width thatdiffers from the first width.